1. Field of the Invention
The present invention relates to a method of cooling an internal-combustion engine and a cooling device thereof. The internal-combustion engine is especially for an automobile.
2. Description of the Related Art
FIG. 10 shows a conventional cooling device where an engine 301 and a radiator 302 are connected with each other by conduits 304 through which a cooling fluid for cooling the engine 301 flows. The cooling fluid receives a flowing force from a waterpump 303. A bypass conduit 305 is connected to the conduits 304 at both an inlet portion and an outlet portion of the radiator 302. When the temperature of cooling fluid flowing out from the radiator 302 is above a predetermined value, the cooling fluid flows in the bypass conduit 305 to bypass the radiator 302. When the temperature of the same is below the predetermined value, a thermostat valve 306 closes the bypass conduit 305 so that the cooling fluid flows into the radiator 302 to be cooled. A heater core 308 is provided in the conduit 304.
In order to cool the engine 301 efficiently, it is required that the cooling efficiency of the cooling device be controlled according to the condition of the engine 301, which varies frequently. The water-pump 303 is driven by the engine 301 and the discharge capacity of water-pump 303 is determined to prevent cavitation of the water-pump 303 and to circulate enough water so that even if the engine 301 is placed under the worst of conditions, such as the automobile going up a slop at a low speed.
Recently, the power of an engine has been increasing and the amount of heat transmitted from the engine to the cooling fluid is also increasing. Therefore, the radiator and the cooling fan are required to be large enough to radiate the heat efficiently. However, the space of an engine room tends to be smaller than ever thereby making it harder to meet such a requirement. One idea to radiate the heat efficiently is to make the discharge capacity of the water-pump larger. However, each increment of the discharge capacity of a water-pump causes an increment of the heat loss of the engine, so that the radiator 302 and the cooling fan 307 become large. When the amount of cooling fluid is increased, the warming up characteristic of the engine becomes worse.
Japanese unexamined patent publication (kokai) 59-28016 shows a cooling device wherein cooling fluid is introduced into a cylinder head and a cylinder block independently. Two streams of the cooling fluid are merged in the cylinder head. The amount of cooling fluid introduced into the engine is controlled by a control valve. However, since a water-pump is driven by the engine, the amount of cooling fluid discharged from the water-pump varies according to the engine rotation, so that enough cooling fluid is not always supplied to the engine. The amount of cooling fluid is determined according to an intake vacuum pressure, a velocity of an automobile and a cooling fluid temperature. The cooling fluid temperature varies especially, according to the course of the cooling fluid and the cooling capacity of the radiator. Namely, the cooling fluid temperature does not always represent a realistic condition of the engine.